The present invention relates to methods for treating the prostate. In particular, the present invention relates to a method of delivering varying amounts of energy to the prostate along the prostatic urethra.
The prostate gland is a complex, chestnut-shaped organ which encircles the urethra immediately below the bladder. The portion of the urethra extending through the prostate (i.e., the prostatic urethra) includes a proximal segment, which communicates with the bladder, and a distal segment, which extends at an angle relative to the proximal segment by the verumontanum.
Although a relatively small organ, the prostate is the most frequently diseased of all internal organs and is often the site of a common affliction among older men, benign prostatic hyperplasia (BPH), as well as a more serious affliction, cancer. BPH is a nonmalignant, bilateral expansion of prostate tissue occurring mainly in the transition zone of the prostate adjacent to the proximal segment of the prostatic urethra. As this tissue grows in volume, it encroaches on the urethra extending into the region of the bladder neck at the base of the bladder. Left untreated, BPH causes obstruction of the urethra which usually results in increased urinary frequency, urgency, incontinence, nocturia and slow or interrupted urinary stream. BPH may also result in more severe complications, such as urinary tract infection, acute urinary retention, hydronephrosis and uraemia.
Benign prostatic hyperplasia (BPH) may be treated using transurethral thermal therapy as described in further detail in U.S. Pat. 5,413,588 entitled DEVICE FOR ASYMMETRICAL THERMAL THERAPY WITH HELICAL DIPOLE MICROWAVE ANTENNA and in co-pending U.S. patent application Ser. No. 08/309,137 entitled COOLANT PRE-CHILLING PRIOR TO BENIGN PROSTATIC HYPERPLASIA TREATMENT, both of which are herein incorporated by reference. During transurethral thermal therapy, the transition zone of the prostate is heated to necrose the tumorous tissue that encroaches on the urethra. Transurethral thermal therapy is administered by use of a microwave antenna-containing catheter which includes a multi-lumen shaft. The catheter is positioned in the urethra with the microwave antenna located adjacent to the hyperplastic prostatic tissue. Energization of the microwave antenna causes the antenna to emit electromagnetic energy which heats tissue within the prostate.
One of the main objectives of transurethral thermal therapy is to selectively deliver a sufficient intensity of electromagnetic energy to the hyperplastic tissues of the prostate to generate necrosis-producing temperatures in those tissues without harming adjacent healthy tissue. In this regard, it is important to avoid thermal damage to urethral, rectal and bladder neck tissues.
Damage to the bladder neck may cause such complications as bladder contractures and trigone damage. Bladder neck contractures occur when the muscle of the bladder neck becomes damaged and as a result contracts and becomes fibrotic. As a result, the opening between the bladder neck and the urethra narrows and possibly closes due to scarring. Occlusion of the opening between the bladder neck and the urethra causes urinary retention. However, removal of scarring to reopen the opening between the bladder neck and the urethra poses a risk of severe infections and bladder stones. In addition, removing scarring often leads to additional new scarring. As a result, bladder neck contractures require continual treatment.
Damage to the bladder wall or trigone occurs when the portion of the bladder wall located between the urethral orifices and the bladder neck is damaged by excessive heat such as that caused by electromagnetic energy. The trigone contains nerves which signal the need for urination. As a result, damage to the trigone causes irritation, dysuria, which is pain upon urination, and possibly hematuria bleeding.